The present invention relates to new grey colouring photochromic fused pyrans and to their use.
Photochromism is a well-known physical phenomenon that is observed with certain classes of chemical compounds. A detailed discussion of this phenomenon can be found in xe2x80x9cPhotochromism: Molecules and systemsxe2x80x9d, Studies in Organic Chemistry 40, Eds. H. Durr and H. Bouas-Laurent, Elsevier, 1990.
The 2H-naphtho[1,2-b]pyran system is known to be capable of exerting a photochromic effect as described, for example, in U.S. Pat. Nos. 3,567,605 and 4,826,977. U.S. Pat. No. 3,567,605 provides an example of a naphtho[1,2-b]pyran which remains coloured at ambient temperatures for several hours, and U.S. Pat. No. 4,826,977 describes a series of yellow/orange colouring 2H-naphtho[1,2-b]pyrans containing a spiro-adamantane group at the 2-position amongst other 2H-[1] benzopyran and isomeric naphthopyran systems. The basic structural unit of the 2H-naphtho[1,2-b]pyran system, in this instance substituted at C-2 with a spiro-adamantane group, is illustrated below. 
A range of purple/blue colouring 2(4-aminophenyl)-2-alkyl-2H-naphtho[1,2-b]pyrans have also been described in U.S. Pat. No. 4,818,096.
A series of photochromic 2H-naphtho[1,2-b]pyrans, amongst other 2H[1]benzopyrans and isomeric naphthopyrans, bearing a cyclopropyl group as one of the substituents at the 2-position is described in patent publication WO92/01959. It is also commented that the compound 2-cyclopropyl-2-p-methoxyphenyl-5-methyl-2H-naphtho[1,2-b]pyran and several other analogues are of particular current interest, but no reasons are presented either to substantiate such interest or as to any significance of the 5-methyl group.
It is stated in U.S. Pat. No. 5,066,818 ( 1991 ) that xe2x80x9cThe compound, 2,2-diphenyl-2H-naphtho[1,2-b]pyran, also colours on exposure to near ultraviolet light at room temperature but does not bleach in a reasonable period of time. Substitution of the phenyl substituents in the meta and para positions have little effect on the rate of bleaching of these compounds.xe2x80x9d
The very high optical density of 2,2-diaryl-2H-naphtho[1,2-b]pyrans achieved under irradiation and their slow attendant fade (bleaching) on removal of the source of irradiation relative to the photochromic properties display:ed by the isomeric 3,3-diaryl-3H-naphtho[2,1-b]pyrans has been noted by B. van Gemert et al. (Mol. Cryst. Liq. Cryst. 1994, 246, 67). The relatively slow attendant fade of the 2,2-diaryl-2H-naphtho[1,2-b]pyrans was rationalised by the absence of steric crowding in the ring opened (coloured) quinoidal/zwitterionic forms. Such steric crowding is thought to be present for the ring opened form of the 3,3-diaryl- 3H-naphtho[2,1-b]pyrans and accounts for their relatively rapid fade.
Pilkington Plc have also commented on the fading of photochromic materials in Research Disclosure {May (1994), No. 36144, p 267}. This disclosure reports that markedly improved rates of fade can be obtained for 2,2-diaryl-2H-naphtho[1,2-b]pyrans bearing substituents at both the 5- and 6- positions compared with 2,2-diaryl-2H-naphtho[1,2-b]pyrans that are unsubstituted at these sites. These substituents are reported to exert steric pressures upon the ring opened (coloured) forms and enhance the ring closure to the uncoloured naphthopyran system. However, these relatively fast fading materials described by Pilkington Plc with substituents at both the 5- and 6- positions are difficult to manufacture, requiring a long multi-stage process which renders them unattractive commercially. Thus the use of two substituents at the 5- and 6- positions to achieve rapid fade in these 2,2-diaryl compounds has the disadvantage of manufacture complexities.
Two more recent U.S. Pat. Nos. 5,458,814 and 5,514,817 describe the synthesis of a range of fast fading intense yellow to red/purple colouring 2,2-diaryl-2H-naphtho[1,2-b]pyrans and phenanthropyrans which either possess a 5-substituent or are 5,6-disubstituted.
Other 5-substituted rapid fading intense colouring photochromic naphtho[1,2-b]pyrans are included in U.S. Pat. No. 5,658,500 (1997). These naphthopyrans, which may also include an aminoaryl group at position 2, can be used in conjunction with other complementary photochromic materials so that together a near neutral grey or brown shade is developed when a lens containing such a mixture is subjected to UV light. Some naphtho[1,2-b]pyrans which may also contain aminoaryl groups at position 2 and are further substituted at position 2,7 and 9 with alkoxy groups have been described in application PCT WO 98/04937. These molecules are attributed with the beneficial properties of higher lambda max values for both of their absorption bands and also have a generally higher induced optical density compared with molecules which do not possess the di-alkoxy substitution pattern.
International patent application WO 95/05382, describes some neutral colouring, typically brown, photochromic heterocyclochromenes in which the hetero ring is fused to either the f- or g-face of the benzopyran unit. No examples or claims pertaining to the h- fused isomers were made. A range of f-fused heterocyclic pyrans has been described in U.S. Pat. No. 5,527,911 (1996). The examples reported in this work all possess unsubstituted phenyl groups at C-2 in the pyran ring and provide orange or red colouring compounds. A subsequent U.S. Pat. No. 5,552,091 (1996) claims f-, g- and h- fused benzofuro-, benzothieno- and indolo- benzopyrans. In all examples, regardless of the mode of ring fusion, C-2 of the pyran ring is substituted with at least one of the following tricyclic moieties: fluorenyl, dibenzofuryl, dibenzothienyl or carbazolyl. No examples of C-2 (monocyclic) diaryl substituents are claimed in this work. An additional PCT, WO 94/20869, also describes f-, g- and h- fusions of benzothiophene and benzofuran to 2,2-diaryl benzopyrans. None of the reported examples pertain to heterocyclic fused 2,2-diaryl benzopyrans in which the pendant aryl groups possess one or more cyclic amino substituents located in the para position.
In International patent application no. PCT/GB98/00904, there are described the synthesis and applications of some neutral colouring (brown or brown/red) photochromic 2,2-diaryl-2H-naphtho[1,2-b]pyrans. The brown or brown/red colouring is obtained by substituting the 2,2-diaryl-2H-naphtho[1,2-b]pyrans in the 7- and/or 9- position with an amino function. The general formula in PCT/GB98/00904 also covers brown or brown/red compounds in which one or both of the 2,2-diaryl groups may be unsubstituted, mono-, di- or poly-substituted and among the possible substitutents are amino, amino C1-C5 alkyl, alkyl C1-C5 amino, dialkyl C1-C5 amino and certain cyclic amino groups. However, there are no specific Examples of such compounds, but only of 2,2-diaryl alkoxy substituted compounds.
We have now found that, surprisingly, photochromic 2,2-diaryl-2H-naphtho[1,2-b]pyrans wherein at least one of the aryl groups is substituted with an amino function, preferably in the para position to the point of attachment to the pyran ring, in addition to amino function substitution at the 7- and/or 9- position, exhibit neutral non-brown, non-brown/red colouring which is quite different from the neutral brown or brown/red described in PCT/GB98/00904. The presence of a 5 substituent in these pyrans may also provide for rapid fading of the colour generated upon irradiation.
The neutral non-brown, non-brown/red colours observed in the photochromic compounds of the invention are typically various shades and hues of grey, blue grey, purple grey, green grey and, on occasion, approach black. They typically result from multiple absorption bands at about 460-520 nm and about 550-650 nm upon irradiation with sunlight or a suitable artificial light source. The bands are often broad and may overlap.
The provision of grey colouring photochromic compounds is highly advantageous. Previously, to achieve, for example, grey colouring, it was necessary to mix two or more compounds. A disadvantage of mixing two or more compounds is that it is very difficult to obtain a uniform grey at all times in the bleach/fade cycle.
The neutral non-brown, non-brown/red, which we shall refer to hereinafter as grey, compounds of the present invention provide photochromic materials with good rates of fade over a broad range of temperatures and intense neutral colour generation accompanied by negligible background colour. These features render these compounds particularly useful as photochromic materials for incorporation into polymeric host materials since the amount of photochromic material required to impart a useful photochromic effect into the host material may be greatly reduced, thereby offering a considerable saving of synthetic effort and cost over conventional materials which do not possess the claimed substitutents.
Examples of applications of the polymeric host materials of the present invention include the manufacture of lenses for sunglasses and ophthalmic lenses, protective visors, screens, films, xe2x80x98plasticxe2x80x99 sheeting, containers (e.g. bottles and other packaging vessels), mirrors, windows and screens for vehicles such as cars (including sunroofs), motorcycles, aircraft and ships, architectural uses e.g. glazing, and artistic xe2x80x98stained glassxe2x80x99 windows and for use in novelty items. Additionally the materials may be used in vehicle body panels including fairings and spoilers, and related external surfaces and other embodiments where it may be deemed attractive to have said objects change colour in the presence of sunlight. A further use is their incorporation into inks and other such formulations for xe2x80x98printingxe2x80x99 onto paper and fabrics and other suitable surfaces. This latter application may be particularly useful for the preparation of security markers (labels) on a broad range of objects e.g. cheques, bonds, bankers drafts, credit cards, charge cards and identity documents and cards. Such inks and other like formulations may be used for printing documents and greetings cards. The security/identity uses of these photochromic compounds may also extend to include the marking of fuels e.g. petrol and diesel and other oils. Furthermore, the materials may be used in optical data recording systems e.g. compact discs, and read/write optical data storage discs, as waveguides and laser dyes.
Typical host materials are optically clear or opaque polymer materials, such as polymers of polyol (alyl carbonate)-monomers, polyacrylates such as polymethylmethacrylates, poly(triethyleneglycol dimethylacrylate), polyperfluoroacrylates and cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, poly(vinyl acetate), poly(vinyl alcohol), polyurethanes, polycarbonate, polyethylene terephthalate, polystyrene, polyfluorostyrene, poly(diethyleneglycol bis(alkyl carbonate)) and various copolymer mixes.
According to the present invention, there is provided a photochromic compound of the formula I 
In formula I above R1 is selected from mono-, di- or poly- substituted aryl groups, mono-, di- or poly- substituted naphthyl groups and mono-, di- or poly- substituted heteroaryl groups (for example but not exclusively thienyl, benzothienyl, furyl, benzofuryl, pyrryl, indolyl, pyridyl, quinolyl, isoquinolyl, pyrimidyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, pyrazolyl, imidazolyl, benzimidazolyl, triazolyl, benzotriazolyl, tetrazolyl). The substituents for the aryl, naphthyl and heteroaryl groups representing R1 are selected from the following nitrogen containing functionalities and are situated preferentially in a conjugating position, typically para to the point of attachment to the pyran ring: amino C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C2-C20 di(polyalkenyl)amino, arylamino, diarylamino, C1-C20 alkylarylamino, tetra(C1-C10 linear or branched alkyl)guanidino and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, linear or branched C1-C20 alkylsubstituted piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N-alkylpiperazino, linear or branched C1-C20 N-hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino). In addition to the above nitrogen containing function, R1 may also possess one or more additional substituents which are selected from hydrogen, linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched C1-C20 haloalkyl, linear or branched C1-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C2-C20 polyalkenyl (any combinations of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched C1-C20 hydroxyalkyl, linear or branched C1-C20 polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched C1-C20 alkylthio, linear or branched C1-C20(C1-C5 alkoxy)alkyl, linear or branched C1-C20(C1-C5 alkylthio)alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, nitrile, carboxyl, C1-C5 alkoxycarbonyl, C1-C5 N-alkylamido, C1-C5 N,N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di(polyalkenyl)amino, arylamino, diarylamino, C1-C20 alkylarylamino, and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, linear or branched C1-C20 alkylsubstituted piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N-alkylpiperazino, linear or branched C1-C20 N-hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino), arylsulfanyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched C1-C20 alkylsulfonyl, di-(C1-C20 alkoxyalkyl)phosphonyl. Phenyl, aryl, naphthyl, and heteroaryl ring substituents may be located at the ortho-, meta- or para- positions. R1 and or R2 may also be selected from the fused saturated heterocycles II, III and IV in which n and m are integers between 2 and 5 and may be the same or different. 
R13 may be selected from linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl, C5-C20 polycycloalkyl, linear or branched C1-C20 hydroxyalkyl, linear or branched C1-C20 haloalkyl, linear or branched C1-C20 perhaloalkyl, phenyl, C1-C20 linear or branched alkylsulfonyi, aryl, tosyl, arylsulfonyl, acyl, linear or branched C1-C20 alkylcarbonyl, benzoyl, aroyl, substituted aroyl, butoxycarbonyl.
R2 is selected from phenyl, mono-, di- or poly- substituted aryl groups, unsubstituted, mono-, di- or poly- substituted naphthyl groups and unsubstituted, mono-, di- or poly- substituted heteroaryl groups (for example but not exclusively thienyl, benzothienyl, furyl, benzofuryl, pyrryl, indolyl, pyridyl, quinolyl, isoquinolyl, pyrimidyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, pyrazolyl, imidazolyl, benzimidazolyl, triazolyl, benzotriazolyl, tetrazolyl). The substituents, of which there may be one or more, for the aryl, naphthyl and heteroaryl groups representing R2 may be hydrogen, linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched C1-C20 haloalkyl, linear or branched C1-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C4-C20 polyalkenyl (any combinations of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched C1-C20 hydroxyalkyl, linear or branched C1-C20 polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched C1-C20 alkylthio, linear or branched C1-C20(C1-C10 alkoxy)alkyl, linear or branched C1-C20(C1-C5 alkylthio)alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, nitrile, carboxyl, C1-C10 alkoxycarbonyl, C1-C10 N-alkylamido, C1-C5 N,N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di(polyalkenyl)amino, arylamino, diarylamino, C1-C20 alkylarylamino, and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, linear or branched C1-C20 alkylsubstituted piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N-alkylpiperazino, linear or branched C1-C20 N-hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino), arylsulfanyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched C1-C20 alkylsulfonyl, di-(C1-C20 alkoxyalkyl)phosphonyl fin addition to those substituents specified for R1. Phenyl, aryl, naphthyl, and heteroaryl ring substituents may be located at the ortho-, meta- or para- positions.
R3 and R4, which may be the same or different, are selected from hydrogen, linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched C1-C20 haloalkyl, linear or branched C1-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C4-C20 polyalkenyl (any combination of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched C1-C20 hydroxyalkyl, linear or branched C1-C20 polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched C1-C20 alkylthio, linear or branched C1-C20(C1-C10 alkoxy)alkyl, linear or branched C1-C20(C1-C5 alkylthio)alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, nitrile, carboxyl, C1-C5 alkoxycarbonyl, C1-C5 N-alkylamido, C1-C5 N,N-dialkylamido, amido, nitro, in addition to those groups specified for R1 and R2 above.
R5 is selected from linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched C1-C20 haloalkyl, linear or branched C1-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C4-C20 polyalkenyl (any combination of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched (C20 hydroxyalkyl, linear or branched C1-C20 polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched C1-C20 alkylthio, linear or branched C1-C20(C1-C10 alkoxy)alkyl, linear or branched C1-C20(C1-C10 alkylthio)alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, linear or branched C1-C20 alkanoyl, linear or branched C3-C20 alkenoyl, linear or branched C5-C20 polyalkenoyl, benzoyl, aroyl, heteroaroyl, nitrile, formyl, carboxyl, linear or branched C1-C20 alkoxycarbonyl, C1-C20 N-alkylamido, C1-C20 N,N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di(polyalkenyl)amino, arylamino, diarylamino, C1-C20 alkylarylamino, and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N-alkylpiperazino, linear or branched C1-C20 N-hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino, N-indolinyl), arylsulfanyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched C1-C20 alkylsulfonyl, di-(C1-C20 alkoxyalkyl)phosphonyl in addition to those substituents specified for R1 and R2 
One or both of R7 and R9, which may be the same or different is selected from C1-C20 N,N-alkylamido, C1-C20 N,N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di(polyalkenyl)amino, arylamino, diarylamino, C1-C20 alkylarylamino, and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N-alkylpiperazino, linear or branched C1-C20 N-hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino, N-indolinyl, N- 1,2,3,4-tetrahydrocarbazolyl, N-1,2,3,4,4a,9a-hexahydrocarbazolyl, N-1,2,3,4-tetrahydroquinolyl). Where only one of R7 or R9 is selected from the above nitrogen containing substituents, the other group R7 or R9 is selected from those substituents specified for R1,R2, R5, R6, R8 and R10.
R6, R8, R10, R11, R12, R14, R15, R17 and R18 which may be the same or different, are selected from hydrogen, linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched C1-C20 haloalkyl, linear or branched C1-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C4-C20 polyalkenyl (any combination of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched C1-C20 hydroxyalkyl, linear or branched C1-C20 polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched C1-C20 alkylthio, linear or branched C1-C20(C1-C10 alkoxy)alkyl, linear or branched C1-C20(C1-C10 alkylthio)alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, linear or branched C1-C20 alkanoyl, linear or branched C3-C20 alkenoyl, linear or branched C5-C20 polyalkenoyl, benzoyl, aroyl, heteroaroyl, nitrile, carboxyl, formyl, C1-C20 alkoxycarbonyl, C1-C20 N-alkylamido, C1-C20 N,N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di(polyalkenyl)amino, arylamino, diarylamino, C1-C20 alkylarylamino, and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N-alkylpiperazino, linear or branched C1-C20 N-hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino, N-indolinyl), arylsulfanyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched C1-C20 alkylsulfonyl, di-(C1-C10 alkoxyalkyl)phosphonyl in addition to those substituents specified for R1 and R2 and R5 
R16 of which there may be one or more, the same or different, are selected from hydrogen, linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched C1-C20 haloalkyl, linear or branched C2-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C4-C20 polyalkenyl (any combination of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched C1-C20 hydroxyalkyl, linear or branched C1-C20 polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched C1-C20 alkylthio, linear or branched C1-C20(C1-C10 alkoxy)alkyl, linear or branched C1-C20(C1-C5 alkylthio)alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, linear or branched C1-C20 alkanoyl, linear or branched C3-C20 alkenoyl, linear or branched C5-C20 polyalkenoyl, benzoyl, aroyl, heteroaroyl, nitrile, carboxyl, formyl, C1-C20 alkoxycarbonyl, C1-C20 N-alkylamido, C1-C20 N,N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di(polyalkenyl)amino, arylamino, diarylamino, C1-C20 alkylarylamino, and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N-alkylpiperazino, linear or branched C1-C20 N-hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino, N-indolinyl), arylsulfonyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched C1-C20 alkylsulfonyl, di-(C1-C10 alkoxyalkyl)phosphonyl in addition to those substituents specified for R1 through to and including R18.
In addition to the 2H-naphtho[1,2-b]pyran compounds of formula I, the present invention includes the pyrans of the general formula V, VI, VII and VIII. 
In addition to the 2H-naphtho[1,2-b]pyran compounds of formula I, the substituents R5 and R6 or R7 and R8 or R8 and R9 or R9 and R10 may each be conjoined by a four carbon unit containing one or more substituents represented by R16 to provide benzo fused naphthopyrans of the general formula IX and X and XI and XII 
In addition to the 21H-naphtho[1,2b]pyran compounds of formula I, the present invention includes the heterocyclic fused pyrans of the general formula XIII and XIV and XV and XVI and XVII and XVIII and XIX. 
The function (X) in the structures XIII-XIX is selected from a single bond, O, S, SO, SO2, Se, NH, Nxe2x80x94O, N-linear or branched C1-C20 alkyl, N-C3-C20 cycloalkyl, N-C4-C20 bicycloalkyl, N-C5-C20 polycycloalkyl, N-linear or branched C1-C10 hydroxyalkyl, N-linear or branched C1-C10 haloalkyl, N-linear or branched C1-C10 perhaloalkyl, N-phenyl, N-C1-C10 linear or branched alkylsulfonyl, N-aryl, N-tosyl, N-acyl, N-benzoyl, N-aroyl, N-butoxycarbonyl, P-linear or branched C1-C10 alkyl, P-phenyl, P-aryl, P- substituted aryl, P(O)-linear or branched C1-C10 alkyl, P(O)O-linear or branched C1-C10 alkyl, P(O)O-phenyl, P(O)O-aryl, Cxe2x95x90S, Cxe2x95x90O, Cxe2x95x90NR16, CH2, CHR16, C(OH)R16, CR17R18.
The function (Y) in the structures XVII-XIX is selected from a single bond, O, S, SO, SO2, Se, NH, Nxe2x80x94O, N-linear or branched C1-C20 alkyl, N-C3xe2x80x94C20 cycloalkyl, N-C4-C20 bicycloalkyl, N-C5-C20 polycycloalkyl, N-linear or branched C1-C10 hydroxyalkyl, N-linear or branched C1-C10 haloalkyl, N-linear or branched C1-C10 perhaloalkyl, N-phenyl, N-C1-C10 linear or branched alkylsulfonyl, N-aryl, N-tosyl, N-acyl, N-benzoyl, N-aroyl, N-butoxycarbonyl, P-linear or branched C1-C10 alkyl, P-phenyl, P-aryl, P- substituted aryl, P(O)-linear or branched C1-C10 alkyl, P(O)O-linear or branched C1-C10 alyl, P(O)O-phenyl, P(O)O-aryl, Cxe2x95x90S, Cxe2x95x90O, Cxe2x95x90NR16, CH2, CHR16, C(OH)R16, CR17R18 
The 1-naphthols and related hydroxy compounds are either commercially available or obtained by known synthetic methods, or derived by such methods by persons skilled in the art of organic synthesis. In particular, the application of the Stobbe condensation to prepare numerous substituted 1-naphthols has been discussed (see Organic Reactions, Wiley, New York, 1951, volume 6, p. 1). Other routes to useful hydroxy compounds include the application of Bradsher cycloaddition methodology e.g. R F. Frank et al., J Chem. Soc., Chem. Commun., 1984, 761.
The synthesis of the propargyl alcohols has been described in the scientific literature, see for example T. F. Rutledge in xe2x80x98Acetylenic Compounds,xe2x80x99 Reinhold, New York, 1968.
The combination of the substituted 1-naphthols and the propargyl alcohols to afford the naphthopyran is well established (Scheme), see for example L. Merlini in xe2x80x98Advances in Heterocyclic Chemistry,xe2x80x99 Academic Press, 1975, vol. 18, p. 159; R Guglielmetti in xe2x80x98Photochromism: Molecules and Systems,xe2x80x99 Studies in Organic Chemistry 40, eds. H. Durr and H. Bouas-Laurent, Elsevier, 1990. chp. 8; J. D. Hepworth, C. D. Gabbutt, B. M. Heron in xe2x80x98Comprehensive Heterocyclic Chemistry A,xe2x80x99 eds. A P Katritzky, C. W. Rees, E. E. V. Scriven, Pergamon, 1996, vol. 5, p. 351. 
The acid catalyst may be selected from alumina (e.g. Brockmann 1), acetic acid, trifluoroacetic acid, silica, clays (e.g. montmorillonite, tonsil), acidic exchange resins, alkylbenzene sulfonic acids (e.g. toluenesulfonic acid).
Organic solvents frequently employed for the reaction include benzene, toluene, xylene, and relatively high boiling alkanes and ethers.
In order that the invention may be more fully understood, reference will now be made to the following Examples, by way of illustration only.